[Relationships between rice empty grain rate and low temperature at booting stage in Heilongjiang Province].

Six major rice varieties (Longdao 3, Kendao 12, Kongyu 131, Longdao 7, Longjing 16, and Songjing 6) in Heilongjiang Province were treated with low temperature 15 degrees C, 17 degrees C, and 19 degrees C for 2, 4, 6 and 8 days at booting stage, and the relationships between their empty grain rate per panicle and low temperature at booting stage were analyzed by using linear interpolation and linear regression methods. In the province, the critical temperature of sterile-type cool injury was 17 degrees C for sensitive varieties, and 16 degrees C for resistant varieties. The most sensitive period of rice to low temperature was 14-18 days before heading. At 15 degrees C for 8 days, the empty grain rate of Songjing 6 and Kendao 12 increased significantly, while that of Kongyu 131 increased less, suggesting that the cold tolerance of Songjing 6 and Kendao 12 was relatively weak, while Kongyu 131 was insensitive to low temperature. There was a significant correlation between the accumulated cool temperature and the empty grain rate of Kendao 12, Longjing 16, and Kongyu 131 (P<0.01). With the increase of accumulated cool temperature, the rice empty grain rate increased significantly, but the increment varied with rice variety.

[Responses of soil humidity on Songnen Plain to climate change in 1980-2005].

Based on the 1980-2005 observation data of ten-day soil humidity, monthly air temperature, and monthly precipitation during crop growth period (from May to September) from 16 agrometeorological stations on Songnen Plain, the spatiotemporal variation of surface soil (0-30 cm) humidity and its responses to the air temperature and precipitation in study area were analyzed by using statistical method. The results showed that on Songnen Plain, the surface soil humidity during crop growth period in 1980-2005 had a decreasing trend, and tended to be aridified, especially in the west and south parts of the Plain. Before the 1990s, the surface soil on the Plain was relatively humid, but thereafter, the humidity kept decreasing, and partial dryness occurred. In the study period, the mean air temperature during crop growth period had a periodical increase before 1992, with a small fluctuation in a cycle of 6 years, but increased obviously after then. The precipitation during crop growth period had a larger inter-annual variation, with a cycle of 4-5 years. The surface soil humidity during crop growth period was significantly negatively correlated to air temperature and positively correlated to precipitation. Both air temperature and precipitation were the main climatic factors affecting the variation of surface soil humidity on Songnen Plain.